(1) Field of the Invention
The present invention relates to an ozone exhaust system for image forming apparatus, and in particular relates to an ozone exhaust system for exhausting ozone arising from a process printing unit of an image forming apparatus.
(2) Description of the Prior Art
In conventional image forming apparatus, voltage application using high voltage sources has been practiced in order to provide electric charge on the photoreceptor in the process printing unit. It is well known that during this process ozone gas will arise from electric field generators (charger wires, needles of needle electrodes, etc.).
Ozone not only has a harmful effect on human body and environment, but also causes damage to photoconductive layers of the photoreceptors used in image forming apparatus. For this reason, there occurs the problem that as a result of aging or depending on the usage history of the image forming apparatus, the photoreceptor become unable to be charged with a correct voltage, inducing local fluctuation in the surface potential thereof, thus causing printing defects such as “printing blur” and “poor sensitivity”.
In order to solve these problems, when air is exhausted from the image forming apparatus, an ozone filter is disposed at the outlet port so that exhaust air meeting the necessary environmental standard will be discharged.
Also, various methods have been proposed for countermeasures against ozone generation: one in which shielding members such as ducts etc. are arranged against the ozone generating source so as to improve ventilation efficiency and remove generated ozone as soon as possible; and one in which members such as photoreceptors etc., which are likely to spoil by ozone are arranged away from the ozone generating source (see Japanese Patent Application Laid-open Hei 04 No. 120556, Japanese Patent Application Laid-open Hei 08 No. 95474).
On the other hand, in the field of recent color image forming apparatus, many kinds of apparatus have been developed which each include multiple process printing units (process printing units for black, yellow, magenta and cyan) unlike a conventional apparatus that include only one process printing unit.
For such a color image forming apparatus, since provision of exhaust ducts and exhaust fans for individual process printing units leads to enlargement and cost-increase of the apparatus, it is a common practice to connect a multiple number of ducts to a single exhaust fan so as to efficiently draw the generated ozone out of the machine to thereby lessen pollution inside the apparatus.
As a typical conventional ozone removal technique, a multiple number of apertures (holes) are formed in the suctioning part of the ducts provided for ozone generating areas so that generated ozone is suctioned into the ducts while fresh air is lead to the ozone generating areas.
The hole size of the apertures are made greater as they become distant from the exhaust fan so as to make the exhaust fan's efficiency (suctioning efficiency) constant.
However, in the conventional technique, there has been a problem that exhaust efficiency unevenness occurs due to the positional relationship between the exhaust fan and process printing units if ozone is tried to be removed at the same time from multiple process printing units by a single exhaust fan.
Thus, a simple arrangement of ducts just considering exhaust in the ozone exhaust system of the conventional image forming apparatus, cannot solve the uneven ozone concentration distribution problem with which parts and components exposed to high-concentration ozone are adversely affected.